It is now widely recognized that gender-based differences can play a major role in the predisposition to disease and injury, yet this remains an understudied phenomenon. Adolescent females who participate in pivoting and jumping sports suffer anterior cruciate ligament (ACL) injury at a 4 to 6-fold greater rate than adolescent males participating in the same sports. Since the passage of Title IX of The Educational Assistance Act, male participation at the high school level has increased less than 3 percent (from 3.7 to 3.8 million), while female participation has increased 800 percent, roughly doubling every 10 years (from 0.3 to 2.7 million). This geometric growth in participation, coupled with the 4 to 6-fold higher injury rate, has been accompanied by an alarming increase in the number of ACL injuries in female athletes. The reason(s) for this ACL injury disparity remain(s) obscure. Prior to puberty, male and female injury risk is more or less equal. Our long-term objectives are to determine how female athletes become more susceptible to non-contact ACL injury, prospectively identify those female athletes who are more susceptible to injury and to determine the underlying mechanistic cause(s) of increased risk at the biomechanical and biochemical levels. Towards these goals, we propose to test the central hypothesis that the biomechanical changes that accompany puberty, including increased height, body segment length and weight, in the absence of the neuromuscular performance spurt that males demonstrate during puberty may lead to biomechanical-neuromuscular imbalances that result in poor dynamic knee stability and high knee injury risk in many female athletes. SPECIFIC AIM 1 will determine if the biomechanical changes that accompany puberty underlie the decreased dynamic knee stability in female athletes. SPECIFIC AIM 2 will determine if specific neuromuscular measures of dynamic knee stability can predict ACL injury risk. These data should provide a foundation for approaching both the mechanistic questions underlying risk disparity, as well as increasing our ability to direct high-risk athletes into appropriate neuromuscular training programs [unreadable] [unreadable]